Interpretive Summary: Transgenic crops have proven commercial utility, but are created using processes known to produce undesirable variability. This variability is known as somaclonal variation. Somaclonal variation affects many genes, and has the result of disturbing the interactions between genes that have been carefully selected by plant breeders to provide top yields and quality. Often, barley plants with somaclonal variation have markedly reduced yields, for instance, which diminishes the usefulness of valuable transgenic traits. Theoretically, repeated cycles of hybridization of transgenic barley plants to non-transgenic plants will eventually result in the transgene being moved into plants that are otherwise complete normal with respect to all other genes. This process is expected to work well, but typically can take three or more years to complete. This research was conducted to discover whether an abbreviated method, one that takes only one year and involves two cycles of hybridization, would eliminate much of the somaclonal variation, as measured by the elimination of yield reductions. The results showed that the original transgenic barley plants had 30% yield losses, but that the plants that had been improved by backcrossing had no or only slight yield losses. This result is very encouraging, because it demonstrates a rapid. way to greatly improve the performance of transgenic barley.

Technical Abstract:
Transgenic crops have proven commercial utility, but are created using processes known to produce undesirable variability known as somaclonal variation. This reduces the utility of transgenic germplasm to the plant breeder, and complicates assessments of transgene-encoded phenotypes. Backcrossing transgenes into a wild type genome is one solution, but producing near-isogenic lines requires a lengthy and resource-intensive process of multiple crosses. However, an abbreviated breeding scheme involving a single backcross to the wild type parent used to produce a transgenic line, which would replace 75% of the variant alleles, should produce transgenic lines with improved performance. Comparisons were made of 'Conlon', primary transgenic lines derived from Conlon, and lines derived from single backcrosses of the primary transgenic lines to Conlon. The primary transgenic lines were different from Conlon for many agronomic and malting characteristics. Most of the backcross-derived lines did not differ significantly from Conlon for most agronomic characteristics. The backcross-derived lines were also similar to Conlon for malting quality traits but showed more differences than for agronomic characteristics. Differences between lines encoding TRI101 versus lines encoding PDR5 suggested that PDR5 insertion or expression may have affected malting quality. It is concluded that a single backcross is an effective, rapid, and inexpensive method for creating superior transgenic lines.